FATIGUE CRACK PROPAGATION MECHANISMS OF CORE-SHELL RUBBER MODIFIED EPOXY RESINS

Epoxy resins are utilized in various industrial areas as adhesives and matrix of composite materials because of the higher stiffness, strength and heat resistance. Toughening with rubber particles is one of the most popular method to enhance the fracture toughness. For the structure uses, the fatigue resistance is very important property as well as the static mechanical properties. In this study the effect of molecular weight between crosslinks (crosslink density) on the fatigue crack propagation properties of rubber-toughened epoxy resin. Several DGEBA epoxy resins with different average molecular weight were used in this study. Core shell rubber (CSR) particles, the diameter of 100nm, were well dispersed in the epoxy. The fracture toughness of Core Shell Rubber-modified epoxy monotonously enhanced with increasing molecular weight between crosslinks, and the effect of core-shell rubber became larger as the molecular weight between crosslink increased. On the other hand, the fatigue threshold had a peak against molecular weight between crosslinks. Whereas there is positive effect of core shell rubber in fatigue resistance for molecular weight between crosslink of 1440g/mol, the fatigue threshold of the core shell rubber modified epoxy is lower than that of unmodified one for molecular weight between crosslinks of 3040g/mol. TEM observation from the side surface of the crack tip revealed that the size of the plastic deformation zone was well related to the fatigue resistance. The core shell rubber particles enhanced the shear plastic deformation region at the crack tip for molecular weight between crosslinks of 1440g/mol, and the particles largely lowered the deformation region. These results was caused by the deformation ability of the epoxy resin under plane-stress state.